This invention relates generally to writing data in a disk drive. More particularly, this invention relates to a method and apparatus for writing data at a constant angular velocity in a disk drive.
Personal computers typically connect to an optical disk drive such as a CD-ROM to read data from a compact disk. On the compact disk, data is stored in the form of pits and lands patterned in a radial track. The track is formed in one spiral line extending from the inner radius of the disk to the outer edge. A pit is a location on the disk where data has been recorded by creating a depression in the surface of the disk with respect to the lands. The lands are the areas between the pits in the tangential direction. The reflectivity of the pits is less than the reflectivity of the lands. To store audio or digital information, the length of the pits and lands is controlled according to a predefined encoding format.
When reading information from the disc, light from a laser beam is directed onto the track and the light beam is reflected back to a photo-sensor such as a photo-diode. Since the pits and lands have different reflectivity, the amount of reflected light changes at the transitions between the pits and the lands. In other words, the encoded pattern of the pits and lands modulates the reflected light beam. The photo-sensor receives the reflected light beam, and outputs a modulated signal, typically referred to as an RF signal, that is proportional to the energy of the light in the reflected light beam.
In FIG. 1, the relationship of the RF signal to the pits 16 and lands 18 is shown. A smaller pit or land decreases both the period and the amplitude of the RF signal. The RF signal in the pits and lands has opposite polarity.
One encoding format used in optical disk systems is eight-to-fourteen modulation (EFM). EFM reduces errors by minimizing the number of zero-to-one and one-to-zero transitions. In other words, small pits and lands are avoided. A one is indicated by a change in the energy of the reflected light beam, that is, a pit edge. A zero is indicated by no change in the energy of the reflected beam for at least two clock periods. Applying the EFM encoding rules, a pit or land will have a length corresponding to the amount of time for at least three and up to eleven clock periods and the electronics will output a corresponding voltage as shown in FIG. 1.
The data is written on the disk via the pits and lands using EFM format. Because of the characteristics of the laser, the media and the recording speed, the EFM signal is adjusted by write strategy electronics which generates laser power control signals that are used to modulate the power of the laser. The write strategy electronics generates the laser power control signals, in addition to other control signals.
The disk controller and disk drive can read data from and write data to disks with a specified constant linear velocity (CLV) at many specified velocities. The term xe2x80x9cNXxe2x80x9d refers to the specified constant linear velocity of the disk with respect to a base constant linear velocity. The base constant linear velocity is the 1X constant linear velocity, and the specified xe2x80x9cNXxe2x80x9d constant linear velocity is equal to xe2x80x9cNxe2x80x9d times the base constant linear velocity of 1X. For example, the specified constant linear velocities include the 1X, 2X, 4X, and 8X constant linear velocities. Typically the specified constant linear velocities are even integer multiples of the 1X velocity.
In FIG. 2, an ideal EFM signal corresponding to a pit or mark that is to be written on the disk is shown. The ideal EFM signal is synchronized to a system clock having a clock period of T. The laser power signal needed to cause the laser to write the ideal EFM signal on the disk is also shown. The write strategy circuit generates the laser power control signals, EFM1, EFM2 and EFM3 that are supplied to laser interface circuitry that are used to generate the laser power signal. FIG. 2 shows the EFM1, EFM2 and EFM3 signals in a CD-Recordable (CD-R) drive. The EFM3 signal controls a low power pre-heat phase of the laser. The EFM2 signal controls the duration of a boost power phase of the laser. The EFM1 signal controls the overall duration of a writing phase of the laser which includes the boost power phase. For the EFM1 signal, the write strategy circuit adjusts the rising and falling edges of the ideal EFM signal in accordance with the write parameters Td and Tr, respectively, and the system clock. For the EFM2 signal, the write strategy circuit adjusts the duration of the EFM2 pulse with respect to the rising edge of the EFM1 signal in accordance with write parameter Tw. For the EFM3 signal, the write strategy circuit adjusts the EFM3 signal with respect to the ideal EFM signal and the system clock in accordance with write parameter Th. To write data accurately, each write parameter, Td, Tr, Tw and Th is adjusted with very high precision, such as {fraction (1/32)} T. In one embodiment, {fraction (1/32)}T is equivalent to 0.9 nanoseconds. The particular values of the write parameters depend, at least in part, on the velocity of the disk.
Using EFM encoding, a 3T symbol is a pulse that has a duration of three clock periods. An 11 T symbol is a pulse that has a duration of eleven clock periods. In CD-ROM disks, the size of the pits and lands for the EFM symbols remains the same across the disk. For example, the length of the pit or land corresponding to a 3T symbol is the same from the innermost radius of the disk to the outermost radius of the disk.
Typically, while an optical disk is being played or read, the optical disk is rotated at the specified constant linear velocity. When the disk is rotated at the specified constant linear velocity and when the head assembly is positioned at the innermost radius of the disk, the disk has a greater angular velocity than when the head assembly is positioned at the outermost radius of the disk. By rotating the disk at a constant linear velocity, the same EFM symbols, such as a 3T symbol, have the same duration when read from any portion of the disk.
Data is also written on the disk at the specified constant linear velocity. Data may be written at different radial positions of the disk. When writing data, if the head assembly is positioned at an innermost track, the angular velocity of the disk will be at a first predetermined value that corresponds to the specified constant linear velocity. When the head is moved to an outer track to write additional data, that data is not written until the angular velocity of the disk is decreased such that the constant linear velocity is maintained. Therefore, writing data at a constant linear velocity incurs latencies while waiting for the velocity of the disk to reach the appropriate constant linear velocity
In view of the foregoing, it would be highly desirable to provide a method and apparatus that reduces the latency for writing data on an optical disk. Such a method and apparatus would allow CD-R and CD-Rewritable (CD-RW) disk drives to write to a disk without waiting for the disk to reach a constant linear velocity
A circuit records data on an optical disk at a constant angular velocity to reduce the amount of time to write data.
A velocity detector determines a velocity of a rotating disk as a detected velocity. A memory stores sets of write signal control values, and each set of write signal control values is associated with a predefined velocity. A control circuit retrieves at least two sets of write signal control values based on the detected velocity and selected predefined velocities of the sets of write signal control values. A write strategy circuit generates one or more write signals in accordance with the write signal control values of the selected set and write data. The control circuit designates a selected set of write signal control values from the at least two sets of write signal control values while the one or more write signals are generated.
In another aspect of the invention, a disc controller uses the circuit to write data on the disk. Yet another aspect of the invention provides a method of recording data on the disk while the disk is rotated at a constant angular velocity.
In an alternate embodiment, position information is used rather than a velocity to determine when to select a different set of write signal control values.
By recording data on the optical disk at a constant angular velocity, the invention reduces the latency of recording data on the optical disk.